1. Field of the Invention
This invention relates to an ink-jet head, an ink-jet-head cartridge, an ink-jet apparatus and an ink-jet recording method for performing recording on a recording material by discharging an ink droplet using a pressure caused by the generation of a bubble.
2. Description of the Related Art
An ink-jet head performs recording on a recording material by generating a bubble by providing a heater with electric energy and discharging an ink droplet using a pressure caused by the generation of the bubble. Ink-jet heads are widely used because of their silent operation, the capability of high-density printing, the ease of color printing, and the like.
In order to stably drive an ink-jet head at a high speed with a high energy efficiency, and to perform high-density recording using an ink-jet head, various attempts have been made.
In order to perform gradation recording using an ink-jet head, Japanese Patent Laid-Open Application (Kokai) Nos. 55-132258 (1980) and 63-160853 (1988) disclose recording-liquid discharging heads in which a heater whose width or thickness has a gradient is disposed within an ink channel, and in which a plurality of heaters are disposed within an ink channel.
In order to efficiently discharge an ink droplet, for example, Japanese Patent Laid-Open Application (Kokai) No. 5-16365 (1993) discloses an approach in which a bubble is made to communicate with the air (atmosphere) while the bubble grows. In this approach, since the distance between a heating resistor and a discharging port is short, the ratio of the work done by the bubble to the electric energy given to the heater is superior to such ratios of previous recording-liquid discharging heads. Furthermore, since almost all ink present between the heater and the discharging port is discharged, the volume of the discharged ink is stabilized.
The above-described conventional approaches, however, have the following problems to be solved.
First, the head which discharges ink by making the bubble communicate with the atmosphere operates rather well when discharging a small ink droplet (equal to or less than 15xc3x9710xe2x88x9215 m3). However, when intending to discharge a relatively large ink droplet, it is necessary to increase the size of the discharging port. As a result, the size of the discharging port greatly exceeds the distance between the heater and the discharging port, thereby providing a flat discharged droplet and causing instability in the direction of ink discharge. Furthermore, the capillary force while refilling ink decreases, thereby increasing the refilling time and preventing of high-speed recording.
On the other hand, in a conventional head in which discharging ports, each for discharging a very small droplet, are arranged at a high density, each of the discharging ports has an ink channel. Hence, each ink channel is narrow, thereby increasing the resistance of the channel and the refilling time.
In the heads in which a heater whose width or thickness has a gradient is disposed within an ink channel communicating with a discharging port and in which a plurality of heaters are disposed within an ink channel in order to perform gradation recording, since there is a correlation between the volume of a discharged ink droplet and the discharging speed, the quality of the recorded image is degraded.
That is, a head is designed to discharge large droplets at appropriate discharging speeds, the discharging speeds of small droplets decrease, thereby causing instability in the direction of ink discharge and in the recorded image. On the other hand, head is designed to discharge small droplets at appropriate discharging speeds, the discharging speeds of large droplets greatly increase, thereby causing splashing when the droplets reach the recording material, and degrading the quality of the recorded image.
It is an object of the present invention to provide an ink-jet head, an ink-jet-head cartridge, an ink-jet apparatus and an ink-jet recording method which can discharge ink at an appropriate speed whether the volume of the ink is small or large and which can refill the ink at a high speed.
It is another object of the present invention to provide a recording-liquid discharging head or the like which can particularly perform high-quality gradation recording.
According to one aspect, the present invention which achieves these objectives relates to an ink-jet head for discharging ink from discharging ports by the generation of bubbles, comprising a plurality of ink channels for guiding the ink to the corresponding discharging ports, and discharging units, each comprising a discharging port, and a heating element, provided for the discharging port, for generating a bubble for discharging the ink by providing the ink within the corresponding ink channel with thermal energy. A plurality of discharging units having different amounts of ink discharge are provided at each of the ink channels.
According to another aspect, the present invention which achieves these objectives relates to an ink-jet-head cartridge comprising the above-described ink-jet head and an ink receptacle for holding the ink to be supplied to the ink-jet head.
According to still another aspect, the present invention which achieves these objectives relates to an ink-jet apparatus comprising the above-described ink-jet head, and recording-medium conveying means for conveying a recording medium for receiving the discharged ink.
According to still another aspect, the present invention which achieves these objectives relates to an ink-jet recording method for performing recording by discharging different amounts of ink from discharging ports, comprising the steps of using a head in which a plurality of discharging units, each including a heating element for generating heat for discharging the ink, and a discharging port for discharging the ink, are provided at each ink channel, and performing recording by discharging different amounts of ink from the discharging ports by selectively driving the plurality of discharging units.
According to the above-described configurations and method, it is possible to discharge ink droplets having different sizes with accuracy, and to achieve gradation recording of a high picture quality. Furthermore, since discharging ports can be arranged at a high density, recordings of higher precision can be achieved.